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Old 11-28-2023, 08:20 PM   #1 (permalink)
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Question Coasting in Neutral vs in Gear DFCO vs no DFCO?

So the generally agreed upon coasting hierarchy is E-Off Neutral, E-On Neutral, E-On Gear, Brakes.

Was wondering where would coasting in gear without DFCO would fall, and if anyone else has experimented with this. I'm uncomfortable with shifting in and out of Neutral too often, so I've been trying out adding just enough throttle to prevent DFCO from activating, and get close to idle's fuel rate. I noticed that the ignition timing readout correlates pretty well with when the engine nearing DFCO (48+), and I combine it with the A/F data (18+ = no fuel) to be sure I didn't back off too far.

I have had the opportunity to test it out on a couple of longer drives, the engine is spinning at a higher RPM than neutral so slightly more internal friction to fight, but I can let the RPM steadily drop so the throttle can be restricted a bit more than idle?

I don't really have a way of testing the travel distance difference between neutral and in gear with fuel, but it's definitely less braking force than DFCO.

Weirdly I can feel the steering wheel vibrate a bit at very low throttle openings. FF drive, so whatever the engine is feeling is bouncing through to the steering column, not sure why. Lugging is too low RPM, right?

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Old 11-29-2023, 12:50 AM   #2 (permalink)
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Quote:
Originally Posted by Appletank View Post
So the generally agreed upon coasting hierarchy is E-Off Neutral, E-On Neutral, E-On Gear, Brakes.

Was wondering where would coasting in gear without DFCO would fall, and if anyone else has experimented with this. Weirdly I can feel the steering wheel vibrate a bit at very low throttle openings. FF drive, so whatever the engine is feeling is bouncing through to the steering column, not sure why. Lugging is too low RPM, right?
Sounds about right.

I often clutch coast in the TSX because N to 6th shifting seems like it would put excessive wear on syncros. Some say that's rough on the clutch, but I have no opinion yet.

Lugging and feeling the result is an indication of harsh operation. Avoid that. Engines operate efficiently at higher RPM where lugging isn't necessary... I probably lug more than I should.
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Old 11-29-2023, 06:22 PM   #3 (permalink)
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Quote:
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Sounds about right.

I often clutch coast in the TSX because N to 6th shifting seems like it would put excessive wear on syncros. Some say that's rough on the clutch, but I have no opinion yet.

Lugging and feeling the result is an indication of harsh operation. Avoid that. Engines operate efficiently at higher RPM where lugging isn't necessary... I probably lug more than I should.
For sure, but IIRC Lugging is when you're at too low RPM and demanding more power than it can give, which the ECU for an automatic probably avoids 99% of the time. I'm not sure I've heard of a danger mode as a result of being at mid-RPM and demanding too little power.

Sure, maybe the engine designers didn't really expect someone to be using the very bottom of the engine map all that often, but you'd think they'd make sure everything within the map runs properly at least?
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Old 11-29-2023, 08:33 PM   #4 (permalink)
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My car has a green light on the dashboard for when it's Okay to short-shift up through the gears.
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Old 11-30-2023, 10:34 AM   #5 (permalink)
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My car has a white light and a black number for what gear it thinks I need to be in for efficiencies. It's usually wrong.
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Old 12-01-2023, 12:50 AM   #6 (permalink)
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I'm ... not sure why people are focused on shifting here, when the original topic was about coasting.
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Old 12-01-2023, 10:20 AM   #7 (permalink)
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Well for me mostly because you were concerned with engine rpm above idle which indicates to me that youre in a gear and maybe lugging engine which was another concern. If you're coasting with the engine disengaged, it won't lug, no major power demands.

Since the just above idle loading practices are rare in typical operation, there is no pressure on designers to remediate odd behaviors with lower gearing and most systems tolerate driveline low rpm slippage to increase rpm and torque
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Old 12-01-2023, 08:26 PM   #8 (permalink)
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Well, assuming an engine running at extremely low torque probably isn't producing much detrimental combustion characteristics, I was mainly asking whether anyone has experimented with very low throttle coasting.

If not, oh well.
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Old 12-08-2023, 08:37 PM   #9 (permalink)
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Quote:
Originally Posted by Appletank View Post
So the generally agreed upon coasting hierarchy is E-Off Neutral, E-On Neutral, E-On Gear, Brakes.

Was wondering where would coasting in gear without DFCO would fall,
Seems to me that if you are adding the engine drag like dfco but keeping the injectors pumping that you are only one step above pushing the gas pedal.
E-on neutral and E-on gear can flip flop around in different conditions such as coasting distance, incline/decline grade%, etc. Dfco (e-on gear) will sometimes be better than e-on neutral since e-on neutral is still using some gas where dfco uses none.
I'm curious about your aversion to neutral coasting. It's a great invention.
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Old 12-09-2023, 03:02 AM   #10 (permalink)
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Older vehicle, sometimes the drivetrain lurches a bit when i shift back to D. Don't want to stress out the transmission clutches too much. I reserve Neutral mostly if I know I'm coasting long enough for the speed to drop considerably, thus transmission and engine RPM dropping with it.

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